Understanding Medical Studies So You Can Get the Prostate Cancer Treatment That’s Right for You

by Gerald Chodak, MD

As you learn about the options
for treating your
prostate cancer, you may
turn to reviewing medical studies. They
will tell you the proportion of men who
are alive, have a stable prostate-specific
antigen (PSA), or did not develop widespread
cancer several years after being
treated. Because they are all published
in medical journals, you probably will
assume that they must be well done and
the results must be reliable. Unfortunately,
that is far from the truth. The fact is,
a great many of the studies that are published
are not well done. That means
the results are unreliable. Without understanding
what makes a study good
or bad and how results are reported, you
run the risk of not getting the treatment
that is right for you.

Medical studies are done in different
ways. The most common types used for
prostate cancer are the following:

A prospective, randomized, controlled
study

A prospective cohort study

A case control, retrospective study

An epidemiological study

Randomly assigning people to their treatment
reduces the chance that the results will be
biased or incorrect.

Dr. Gerald Chodak

Prospective, Randomized, Controlled
Study
This type of study is by
far the best because it gives the most
reliable information. To understand
the reason, you must first know what
each word means.

Prospective means the study was
carefully designed before anyone
was treated.

Randomized means that at least two
treatments are being compared to each
other, and neither the participant nor the
doctor can choose what treatment to
receive. A computer will make this decision.
Randomly assigning people to
their treatment reduces the chance that
the results will be biased or incorrect.

Controlled means only people with
specific characteristics are allowed to
enter the study, and everyone is supposed
to be managed in the same way. They all
get the same tests before and after they
are treated, and the treatments are standardized.
For example, if surgery is being
compared to external radiation, every
person in the radiation group gets the
same amount of radiation, and it is delivered
using the same technique.

When done properly, a prospective,
randomized, controlled study is the
only reliable way to prove that one
treatment is as good, better, or worse
than another treatment. All new drugs
must be tested in this way to gain
approval from the Food and Drug Administration.
Unfortunately, prospective,
randomized, controlled studies are very
expensive to do, and they can take many
years to complete. Without these studies,
doctors are unable to determine
which therapy is best.

Cohort Study
A cohort study also
is prospective, but it differs from a randomized
study in that all the individuals
get to choose their treatment. For example,
if a doctor wants to study the
effect of a radical prostatectomy, any
man healthy enough to undergo an
operation can decide to participate.
Specific information about each person
is recorded, and then they are followed
to see what happens to them. The
results are compared with other treatments
published in medical journals.

Cohort studies are easier to do than
prospective, randomized, controlled
studies, which is partly the reason why
more of these studies are done. The
problem with comparing cohort studies
is that the results can be very biased,
leading to incorrect conclusions. Using
these results to compare different treatments
may suggest that they are similar,
but only a prospective, randomized study
can prove if that is true.

Retrospective, Case Control Study
This study design collects information
from medical records about men who
had their treatment
sometime
in the past. The
results are then
analyzed and
compared to
other studies.
The value of
retrospective
studies is that
they are relatively
easy to do,
are not very costly, and can give immediate
information without having to wait
many years to get results. Unfortunately,
retrospective studies often lead to incorrect
conclusions for several reasons:

There is no way to be sure that the
information entered into the chart is
correct. Errors are common, and there
is no way to correct them.

Because the study was not prospective,
everyone may not have been treated
in exactly the same way. For example, in
a retrospective study of men having a
radical prostatectomy, some of them also
may have received radiation or hormone
therapy. Combining them with men only
having surgery will distort the results.

Some men having the treatment may
be excluded because of missing information.
This creates a selection bias, which
can make the results appear better than
if all the men treated were included.

Allowing men to select their treatment
also can create a bias, making the results
appear better than if a randomized study
was done.

When the results of two retrospective
studies are compared, the characteristics
of the participants rarely are the same,
which can lead to misleading conclusions.
It would be like trying to compare apples
to oranges to decide which fruit is sweeter.

Because of these potential weaknesses,
the results of case control, retrospective
studies cannot be used to make reliable
conclusions. This does not mean that the
results are definitely wrong, but there is
no way to be sure that they are correct.
For that reason, you should use caution
when told about the results of a retrospective
study.

Epidemiological Study
This also is
a retrospective look at what happened
to a group of individuals treated in the
past. Information is collected from
the medical records and then fed into
a computer. It searches for anything
that separates individuals into those
who did well and those who did poorly.
For example, consider a group of men
who were all treated in the past by external
radiation. When the results are
analyzed, the study may find a higher
survival rate in men who took vitamin
C compared to those who did not. The
study would then conclude that vitamin
C improves survival of men having external
radiation.

Is this conclusion valid? Does it mean
that men having radiation should be advised
to take vitamin C to improve their
survival? The answer is no, it is not a
valid conclusion or recommendation.
Epidemiological studies can suggest
vitamin C may be beneficial, but only
a prospective, randomized, controlled
trial can prove if that is true. There can
be many other explanations why some
men did better than others that have
nothing to do with taking this vitamin.

Epidemiological studies are much
easier to do than prospective, randomized,
controlled studies, and they are often
mentioned in the news. The problem is
that the results are made to appear reliable,
and the weakness of the study
design is rarely reported. You should be
very cautious when making decisions
based on epidemiological studies.

The Bottom Line
The main message
here is that some results reported
to you come from well-designed studies,
and other results come from poorly designed
studies. The better the study design,
the more you can trust the results.

♦ ♦ ♦ ♦ ♦

Dr. Gerald Chodak performed the first
laparoscopic lymph node dissection for
prostate cancer in Sweden, Finland, Norway,
and Japan. He helped form the first
chapter of Us TOO, an international support
group for men with prostate cancer
and their significant others. Currently, he
produces a weekly video for Medscape.com
called “Controversies in Urology” and
maintains a prostate educational website
at ProstateVideos.com.